An enzymatic tandem reaction is described in which the enzymes phosphorylase and Deinococcus geothermalis glycogen branching enzyme (Dg GBE) catalyze the synthesis of branched polyglucans from glucose‐1‐phosphate (G‐1‐P). Phosphorylase consumes G‐1‐P and polymerizes linear amylose while Dg GBE introduces branching points on the α‐(1 → 6) positions by reshuffling short oligosaccharides. The resulting branched polyglucans have an unusually high degree of branching of 11%.
CdSe nanoparticles stabilized with the amphiphilic diblock copolymer polystyrene‐block‐poly(4‐vinylpyridine) were spread from toluene dispersion on the water surface. Monolayers could be transferred onto solid substrates using the Langmuir‐Blodgett technique. By means of atomic force and scanning electron microscopy highly symmetric ring and disk‐like structures with diameters ranging between 150 nm and 1200 nm were observed.
AFM image of a mixed monolayer of copolymer 12 and CdSe nanoparticles stabilized with polystyrene‐block‐poly(4‐vinylpyridine). 相似文献
Homogeneous surface coating of multi‐walled carbon nanotubes is achieved for the first time by in situ copolymerization of ethylene (E) and 2‐norbornene (N) as catalyzed directly from the nanotube surface previously treated by a highly active metallocene‐based complex, i.e., rac‐Et(Ind)2ZrCl2/MMAO‐3A. The copolymerization reaction allows for the destructuration of the native nanotube bundles, which upon further melt blending with an ethylene–vinyl acetate copolymer (27 wt.‐% vinyl acetate) matrix, leads to high‐performance polyolefinic nanocomposites. The microstructural analysis of the surface‐coating copolymer was carried out by 13C NMR spectroscopy and allowed determination of the actual N content incorporated along the chains. Depending on the experimental conditions used (e.g., E pressure, solvent, feed N concentration) the relative quantity of E–N copolymer can be tuned, as well as the N content in the formed copolymers and accordingly their glass transition temperature.
Amphiphilic H‐shaped block copolymers (PTMSPMA)2PEG(PTMSPMA)2 with 91 ethylene glycol (EG) units and four PTMSPMA chains have been synthesized by atom transfer radical polymerization of trimethoxylsilylpropyl methacrylate (TMSPMA) at room temperature in methanol. The structure, molecular weight, and molecular weight distribution have been characterized by 1H NMR spectroscopy and GPC traces. These H‐shaped block copolymers can self‐assemble in DMF/water, and multiple vesicle aggregates from large‐compound vesicles, to multilayer vesicles and unilamillar vesicles are formed. These morphologies can be simply controlled by variation of the chain length ratios.
Summary: Experimental and modeling studies of addition–fragmentation chain transfer (AFCT) during radical polymerization of methyl methacrylate in the presence of poly(methyl methacrylate) macromonomer with 2‐carbomethoxy‐2‐propenyl ω‐ends (PMMA‐CO2Me) at 60 °C are reported. The results revealed that AFCT involving PMMA‐CO2Me formed in situ during methyl methacrylate polymerization has a negligible effect on the molecular weight distribution.
Summary: This contribution describes the graft polymerization of polystyrene (PS) by atom transfer radical polymerization at 50, 60, and 75 °C. Thick PS brushes were grown from initiator‐functionalized PGMA layers on silicon, and constant growth rates provide indirect evidence that the polymerizations were controlled.
Formation of polystyrene brushes at T < Tg by ATRP of styrene from α‐bromoester initiator‐functionalized poly(glycidyl methacrylate) layers. 相似文献
A novel terminal modification agent to endow hyperbranched polyamidoamine (HPAMAM) with thermo‐/pH‐responsive properties is reported. HPAMAM with terminal vinyl groups is first synthesized and then end‐capped by 1‐adamantylamine (ADA). The resulting hyperbranched polymer (HPAMAM‐ADA) shows interesting thermo‐responsive properties in aqueous solution, which have been investigated by UV‐vis spectroscopy, optical microscopy, and 1H NMR spectroscopy. The lower critical solution temperature can be controlled by adjusting the end‐capping ratio of ADA. In addition, HPAMAM‐ADA exhibits a pH‐dependent water solubility. This pH‐responsive behavior is also studied.
Summary: This paper presents the structural influence of the Si H functionality on the physicochemical properties of polysilanes. New low‐temperature restructuring processes were discovered using thermal analysis (TGA, DSC). Photoluminescent (FL) and X‐ray photoelectron spectroscopy (XPS) measurements revealed the optoelectronic properties‐chemical structure relationship of the synthesized polymers.
Highly reactive Si H groups lead to restructuring of the main polysilane chain. 相似文献
Novel tboc‐protected ionenes with exceeding 30 kDa were prepared from the step‐growth polymerization of tert‐butyl bis[3‐(dimethylamino)propyl]carbamate and 1,12‐dibromododecane. The protected ionenes yielded pH‐sensitive, protonatable ionenes with pKa ≈ 6.6 for the conjugate acid of the protonated secondary amine. Polyplexes of the protected and deprotected ionenes, whose cytotoxicity for endothelial cells was analyzed using the MTT assay, efficiently complex plasmid DNA. Polyplexes destabilized cellular membranes as revealed using the lactate dehydrogenase assay at high concentrations. The polyplexes were successfully transfected into HBMECs at mass ratios 2, 4, 8, 12, and 16 (polymer/DNA) at polyplex concentrations less than 10 µg · mL?1.
A new semi‐analytical approach to model simultaneous chain scission and branching is described that assumes the separation of the scission and the branching problem. The required properties of the linear segments or primary polymers forming the branched architectures are found by a kinetic model. The general rules for the construction of branched architectures from populations of linear segments then lead to an analytical expression for the branching distribution and a semi‐analytical expression for the bivariate length/branching distribution. The method is applied to the scission of an initially branched polymer and subsequent terminal branching on scission points and activated terminal double bonds. Exact agreement is found with Monte Carlo sampling results.
The catalytic behavior of three bis(phenoxy‐imine) group‐4 transition‐metal complexes (M = Ti, Zr, Hf), with iBu3Al/Ph3CB(C6F5)4 cocatalyst systems towards propylene polymerization was investigated under atmospheric pressure at 25 °C. The Ti complex produced ultrahigh‐molecular‐weight atactic poly(propylene), whereas Zr and Hf complexes formed high‐molecular‐weight isotactic poly(propylene)s via a site‐control mechanism. The isotactic poly(propylene) obtained with the Hf complex displayed a high melting temperature of 123.8 °C.
The mechanistic interpretation of kinetic anomalies in reversible addition–fragmentation chain transfer (RAFT)‐mediated polymerization is critically reviewed. The main conclusion of this exercise is that available data do not allow model discrimination between the two prevailing mechanistic schemes, i.e., the slow fragmentation model and the intermediate radical termination model. However, assessment of the rate parameters reveals that the incompatibilities may not be as large as previously reported in literature. Dedicated kinetic studies on model compounds should be performed to shed further light on the seemingly incompatible data that currently exists in literature.
We report the synthesis of glycosylated hydrogel membranes of poly{[N‐(2‐hydroxypropyl)methacrylamide]‐co‐(2‐hydroxyethyl methacrylate)} with the aim of developing bioactivated polymer substrates for cell culture. 3′‐Sialyllactose, the saccharidic portion of the GM3 ganglioside involved in cell‐cell recognition over a wide range of biological processes, was chemically modified with an acrylate group and incorporated into the growing macromolecular network of hydrogels by free radical crosslinking copolymerization. The incorporation and accessibility of the sialic acid residues at the hydrogel surface was verified by enzyme linked immunosorbent assay using mouse monoclonal anti‐GM3, and by electron microscopy after labeling with lectin‐gold nanoparticles. The water content was further characterized by thermogravimetry.
The execution of individual KMC events can become a major computational bottleneck in the simulation of sequences along chains using KMC because of complex data storage schemes required to record the sequence of each chain. The execution of a KMC event can be very time‐consuming because searching, moving, and modifying all the data detailing a chain to reflect the transformation as a result of a chemical reaction event can be computationally expensive. To address this issue, we developed a new data storage scheme for recording sequence, which can significantly improve calculation speed without affecting the information content of the calculations. By using the proposed data storage scheme, the computational time can be reduced significantly from 12 h to 4 min for our test reaction system.
The synthesis and characterization of a soluble high molecular weight copolymer based on 4,8‐bis(1‐pentylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene and 2,1,3‐benzoxadiazole is presented. High efficiency organic photovoltaic (OPV) devices comprised of this polymer and phenyl‐C71‐butyric acid methyl ester (PC71BM) were fabricated by additive processing with 1‐chloronapthalene (CN). When the active layer is cast from pristine chlorobenzene (CB), power conversion efficiencies (PCEs) average 1.41%. Our best condition—using 2% chloronapthalene as a solvent additive in CB—results in an average PCE of 5.65%, with a champion efficiency of 6.05%.
Summary: The interactions between poly{(2,6‐pyridinylenevinylene)‐co‐[(2,5‐dioctyloxy‐p‐phenylene)vinylene]} (PPyPV) and SWNTs have been investigated using UV‐Vis absorption spectroscopy. The SWNTs promoted polymer organization. PPyPV is a Lewis base and can be doped by strong and weak Lewis acids. The basicity strength of the PPyPV depended on the polymer interchain interactions, which were enhanced by the presence of SWNTs. As the SWNT concentration was increased, an increment in the Kb of PPyPV was observed.
Highly efficient and well‐controlled ambient temperature reversible addition–fragmentation chain transfer (RAFT) polymerization is readily carried out under environmentally friendly mild solar radiation. This discovery has significantly extended studies from man‐made separated‐spectroscopic‐emission UV‐vis radiation (Macromolecules 2006 , 39, 3770) to natural continuous‐spectroscopic‐emission solar radiation for ambient temperature RAFT polymerization.
A novel heat‐sealing performance is achieved by polyethylene (PE) nanocomposites reinforced by ethylene vinyl acetate (EVA) and montmorillonite (MMT). Appropriate nanocomposite design leads to hermetic seals with a general peelable/easy‐open character across the broadest possible sealing temperature range. Observations of the fracture seal surfaces by infrared spectroscopy and electron microscopy reveal that this behavior originates from a synergistic effect of the EVA copolymer and the montmorillonite clay nanofiller. Namely, the combination of EVA‐copolymers and MMT nanofillers provides sufficiently favorable interactions for nanocomposite formation and mechanical robustness, but weak enough interfacial adhesion to promote a general cohesive failure of the sealant at the EVA/MMT interfaces.
